1- IJME-Analysis of Scavenging Parameters in Two Stroke Engine

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The SI engines are of extreme importance to the automobile industry. The efficiency of the SI engine depends on several complicated processes, including induction, mixture, preparation, combustion, and exhaust flow. Externally scavenged engine is developed in I.C. Engine laboratory to eliminate short-circuiting losses and reduce the pollutant emitted by engine cylinder. This work deals with comparative experimental investigations carried out on a single cylinder two stroke S.I. Engine in carburetor mode with normal and modified scavenging system. The focus of the research presented in this paper is to estimate the scavenging parameters of a two-stroke externally scavenged engine by measuring various factors such as delivered charge, scavenging efficiency, retained mass, swept volume, delivery ratio, etc. Effects of external scavenged system on performance and emissions of two stroke engine are investigated at different loads and speeds by scavenging parameter calculations. Performance of externally scavenged engine is compared with crank-cased scavenged engine. Result show that scavenging efficiency and delivery ratio of modified engine is improved due to supply of leaner air-fuel mixture to the engine. The most outstanding result of using the external scavenged system is the significant reduction in the retained mass from engine.
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  www.iaset.useditor@iaset.us ANALYSIS OF SCAVENGING PARAMETERS IN TWO STROKE ENGINE  Mohammad Ayaz Afsar 1 &A. M. Mahalle  2 1  MechanicalEngineering Department,Government Polytechnic,Amravati,Maharashtra,India 2  Reader Laxminarayan Institute of Technology, Nagpur,Maharashtra,India  ABSTRACT  The SI engines are of extreme importance to the automobile industry. The efficiency of the SI engine depends onseveral complicatedprocesses, includinginduction,mixture, preparation, combustion, and exhaust flow. Externally scavenged engineis developed in I.C.Engine laboratory to eliminate short-circuiting losses and reduce the pollutant emitted by engine cylinder. This work deals with comparative experimental investigations carried out on a singlecylinder two stroke S.I. Engine in carburetor mode with normal and modified scavenging system. The focus of the research presented in this paper is to estimate the scavenging parameters of a two-stroke externally scavenged engine by measuringvarious factors such as delivered charge, scavenging efficiency, retained mass, swept volume, deliveryratio, etc.Effects of externalscavenged system on performance and emissions of two stroke engineare investigatedat different loads and speeds by scavengingparametercalculations.Performance of externally scavenged engine is compared with crank-cased scavenged engine.Result show thatscavenging efficiencyand delivery ratio of modified engine is improved due to supplyof leaner air-fuel mixture to the engine.The mostoutstandingresult of usingthe external scavenged systemis thesignificant reduction in the retained mass from engine.  KEYWORDS: SI Engines, Scavenging Efficiency, Scavenging Parameters, Exhaust Emission  Article History Received:03 Jan 2018| Revised:12 Feb 2018| Accepted:19Feb 2018 INTRODUCTION The function of scavenging is the removal of the products of combustion from the engine cylinder by fresh aircharge in preparation for the next working cycle. This process is common in all internal combustion engines. If thescavengingprocess is not proper,then there may be loss of power [3]. It also tends to increase in fuel consumption. So itbecomes necessary to study the scavenging process to avoid the loss.A detailed study of scavenging process is required toanalyzethe performance and scavenging parameters.This paper presents an experimental analysis of various scavenging parameters for various speed and load conditions.Experimentationis carriedout on the modified engine in which a passage is made in the block for air aspiration to avoidthe short-circuiting in the engine cylinder. So the process of scavenging is effective. International Journal of MechanicalEngineering (IJME)ISSN (P):2319-2240; ISSN (E):2319-2259Vol.7, Issue2,Feb-Mar2018;1-8© IASET   2Mohammad Ayaz Afsar & A. M. Mahalle Impact Factor (JCC): 4.9345NAAS Rating 3.30 SCAVENGING PARAMETERS To facilitate open discourse of two-stroke engine-related research and design, a large body of standardterminology has been created. This section will give a summary of the standard definition of terms that will be used todescribe experimental configurations andthe resultslater in this text.The delivery ratio is defined as the ratio of the mass delivered to the mass the displaced volume of air has atambient conditions,Whereis the mass of air delivered,is the volume swept by the piston each crankshaft revolution,andis the density of air at ambient conditions.Scavenging eff  iciency, η is defined as the ratio of mass of retained charge to the mass the total mass trapped in cylinder:-It can be calculated asWhere,is the delivery ratio.The trapping efficiency is defined as the mass fraction of thedelivered charge that is retained. It can also beexpressed as the ratio of the charging efficiency to the deliver ratio.It can be measured by the general equationCharging efficiency,, relates the retained portion ofthe deliveredcharge to the swept mass. It is measured by ENGINE SPECIFICATION Table1Technical Specifications of the Engine UnderConsideration Peak power8.0 hp at 5500 rmpHighest power amongst 2-stroke scootersPeak torque1.35 Kgm at 3500rpmInstantaneous pick-up Engine Type5-port single cylinder, 2-stroke with reedvalve inductionAdvanced engine for superior performanceTransmission4-speed gear boxSmooth easy shiftingClutchWet multi-disc typeOperating cycleTwo-stroke spark ignition, 150 cc engineCompression ratio6-10Bore0.05-0.085 mStroke/bore ratio1.2-0.9Max rated BMEP4-10 AtmWt/power ratio5.5-2.5Appr. Best Bsfc350 (gm/kw hr)   Analysis of Scavenging Parameters in Two Stroke Engine3 www.iaset.useditor@iaset.us EXPERIMENTAL SETUP The Experimental setup consist of a 150cc twostroke,one cylinder S.I.Engine,an engine test bed and an exhaustanalyzer. The schematic of the Experimental setup is shown in the figure 1.Specification of the base engine are given inTable 1.A view ofthe test bedis shown in figure 2.The Eddy current dynamometeris used to measure the torquedeveloped by the engine.The engine speed is noted and useful or brake horsepower may be calculated.an exhaust gasanalyzeris used in this experiment.The DELTA 1600Sanalyzeris used to measure exhaust gases.It is small and lightweight analyser.Itsresponsetime is 15s and flow rate approximately 1.2l/min. Figure1: Experimental Setup 1.Control Unit2.Air Box3.Carburattor4.Fuel Meter5.Crankcase6.Engine7.Dynamometer8.Tachometer9.SpringBalance10.Air BoxforScavenged Air11.Manometer12Burrete13.Exhaust Gasanlyser14.Direct AirAspiration Figure2: SchematicDiagramof Experimental Setup PLANNING OF EXPERIMENTS ã The first phases of investigation consist of evaluation of performance of engine to form base for furthercomparisons. This included the measurement ofBrakePower, BSFC, exhaust gas temperature, HC and.CO atdifferent load and speed. ã The second phaseofthe investigationconsisted of modification ofthe base engine. Crank cased scavenged engineis converted intoexternalscavenge engine. Scavenging port was designed so as to aspirate external air insideengine cylinder.The scavenging port diameterwas calculated based upon volumetric efficiency and otheroperatingparameters. This optimum diameter of scavenging port allows air to pass to combustion chamber so asto evacuate it with exhaust gases for better scavenging.   4Mohammad Ayaz Afsar & A. M. Mahalle Impact Factor (JCC): 4.9345NAAS Rating 3.30 ã In the third phase of investigation performance parameter ofthe external scavenged engineis evaluated.This included the measurement of BP, BSFC, exhaust gas temperature, HC and CO at different load and speed. ã In the fourth phase of investigation performance characteristic and exhaust emission ofbaseengine wascompared. Improvement in the performance characteristic and exhaust emissions were noted. All the tests wereperformed at constant speed and variable load and vice  –  versa. RESULTS AND DISCUSSIONS The variation of brake thermal efficiency with Brake power forthe normal and modified engineis shown inFigure3. It is seen that Brake Thermal Efficiency of modified engine is more than normal engine in all cases. This increasein Brake Thermal Efficiency for modified engine is attributed tothe higher oxygen contentin the combustion chamber duetothe extra airaspired bythe engine. This air aspiration improvesthe combustion processwhich leads to higher brakethermal efficiency.This is due to reduction in short-circuiting losses andan increasein air-fuel ratio. Air-fuel ratio can bemadeslightly leaner by supplying extra air through the extra port.It indicates that the engine can operate in leaner air fuelratio without loss of power. This is achieved,because of precise timing and design of externally scavenged port inmodified engine. Figure 3:VariationofThermal EffeciencywithBrake Power The folowing graphs were also drawn for the performance evaluation of an engine for evaluating scavengingparameters. ã Speed Vs Delivery Ratio ã Speed Vs Scavenging Efficiency ã SpeedVs Trappingl Efficiency ã SpeedVs Charging Efficiency
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